Electricity + Control August 2017

• Harmonics: These generally result from the load source and propagate themselves back into the local and distribution networks. De- pending on the type and severity of the har- monic, it can result in over heating of the neu- tral conductors, premature tripping of circuit breakers and possible reversing of electrical motors. The harmonics also influence the pow- er factor of the plant and can be responsible for the failure of the PFC capacitor circuits With these quality of supply problems, it’s easy to see that simply having a back-up power solution isn’t enough. Businesses that rely on power – and, let’s face it, they virtually all do – can find themselves faced with more than just a power outage. Damage caused by surges, sags, spikes and harmonics can costs businesses hundreds of thousands of rand in equipment repair and loss of productivity. UPS – the answer? UPSs are seen as the ‘one solution fits all’ option to protecting equipment and, while that’s not entirely true, it’s also not quite so simple. There are a lot of factors that influence what type of UPS is required, such as the nature of the equipment being sup- ported, the load, how critical maintaining constant power supply is, and the electrical environment, as indicated above. As can be seen from above, one requires continuity of supply, voltage stabilisation, filtration for the spikes and harmonics and galvanic isolation in order to be called a power conditioner. There are essentially three types of UPS, start- ing with the most basic, which is your offline UPS. These, offer just enough time to shut down equip- ment – usually 3 – 4 minutes and are commonly used to support things like office computers. This type of UPS offers limited protection from surges or voltage instability and are as susceptible to be- ing damaged themselves by poor quality power. The second type is your line interactive UPS, which has a small amount of power conditioning built in, such as voltage stabilisers to help regulate input power and has an element of line filtering and surge protection to reduce spikes and dips. Very

popular in small IT environments, these units are reasonably priced and typically offer about 15 min- utes of back-up time – just enough to facilitate auto- matic shutdowns of systems and servers. Howev- er, the extent of power conditioning is still limited. The last type of UPS technology is the true, on- line double conversion UPS, which is designed to run 24 hours per day, with large battery banks for extended back up during power failures.These UPSs act as intermediaries between the grid and equip- ment, offering good power conditioning and can tol- erating most surges, sags and fluctuations in supply. However, experience and the results of many site surveys have shown that UPSs are not com- pletely effective on their own, and need to be sup- ported by additional power conditioning equipment such as voltage stabilisers for extreme fluctuations in input voltage. The use of isolation transformers, offers very good common mode protection and can help to reduce or increase incorrect supply voltage conditions and are able to contain harmonic condi- tions in a network. It is also important to understand that a UPS is not a lightning protector and that a lightning protection device should be added to all UPS installations to protect both the load and the UPS from failure due to excessive lightning activity. Conclusion Finally, it is very important to refer to the UPS man- ufacturers electrical and environmental operating specifications, as too often the level of harmonics present and the extreme deviation of the power factor from unity can result in the inability of the UPS to function correctly and results in both the load and UPS being permanently damaged.

Businesses, particularly those for which quality of supply is critical, must plan their solutions properly.

<>

Kevin Norris, Solutions Architect, Jasco Power.

makwe.ngwato@jasco.co.za www.jasco.co.za

Electricity + Control

AUGUST 2017

13